Reinforced cylinder head

Abstract: A cast cylinder head of light metal incorporates a reinforcement made of a stronger material than the light metal. The reinforcement consists of a relatively narrow elongated steel plate (6) which stretches in a single piece along all the cylinders. The elongated steel plate (6) is provided with transverse arms (8) which stretch out approximately perpendicularly from the steel plate between the valve port apertures (3a, 4a, 5a, 6a) of each cylinder.

Description: The invention relates to a reinforced cylinder head which is for a combustion engine and which is cast in a light metal alloy such as aluminium and aluminium alloys. STATE OF THE ART Development work is continually going on within the vehicle industry with a view to improving the ratio between the power output and weight of vehicle engines. This endeavour has resulted inter alia in improvements with regard to the geometrical design of combustion chambers, ignition control and further development of the fuel supply and exhaust gas systems. The majority of today's combustion engines thus incorporate several inlet and exhaust gas ports per engine cylinder; there are normally four ports comprising two inlet ports and two exhaust gas ports for each cylinder. These ports are usually arranged symmetrically in a four-leaf clover pattern about the central axis of each cylinder. In parallel with the endeavour to increase engine power output, there has been an endeavour to reduce engine weight. The weight decrease which has been achieved and which has led to light combustion engines has primarily arisen because it has been possible for new casting material consisting of high-quality light metal alloys to be used for making engine castings. The weight reduction is offset, however, by the fact that the endeavour to increase engine power output involves, for example, a larger number of valve ports and mechanical weakening of the cylinder head. There is therefore an interdependence between the two endeavours. Increasing the engine power output requires better strength characteristics in the material used, which tends to conflict with the desire to reduce engine weight. Modern high-quality light metal alloys have a substantial disadvantage in that they are considerably more expensive than traditional materials, thereby increasing engine production costs. In combustion engines the greatest material stresses occur around the cylinders, since it is precisely in this area that the thermal and mechanical load gradients are greatest. In multi-valve engines the strength problem is further exacerbated by the fact that the ports have of necessity to be located here, which reduces the volume of material available for power absorption and heat dissipation in the most exposed area. OBJECT OF THE INVENTION The object of the invention is to indicate a solution which results in better utilisation of material from the strength point of view, so that the light metal material is relieved of stress in the most exposed areas, so that the same engine power output can be extracted while using a less expensive alloy material or a higher power output can be extracted while continuing to use a high-quality casting material. This is achieved with a cylinder head of the type defined in the introduction by incorporating an elongated reinforcing plate which is made of a mechanically stronger material than the light metal and is embedded in the light metal so as to stretch in a single piece along all the cylinders. The arranging of some form of insert around each cylinder was certainly already known in the 1950s. The real purpose of those inserts is not to provide the host material with greater mechanical strength but simply to use each insert, which ends directly in the cylinder space, to fill the cavity in which it is inserted in order to prevent the latter becoming choked with the residual products which arise from combustion. It is thus the cavity and not the insert material which is primary in the prior art. The cavities stretching to the combustion chamber serve as expansion joints, the primary function of which is to prevent the propagation of cracks which may arise in the material as a result of the great temperature differences which occur in the area around the cylinders. An example of such a design appears in DE,B, 1 001 860, in which thin sheetmetal rings are arranged concentrically in the area around a cylinder. It also emerges from that publication that various materials are used in this connection, such as mica or thermoplastics, which are known to have no capability for mechanically strengthening the material. The sheetmetal rings which in that publication replace mica or thermoplastic inserts are therefore not intended to absorb any substantial forces. A similar arrangement is described in US,A, 4 337 735, which is more recent by approximately thirty years. This involves a more developed technique using steel inserts to prevent crack propagation, in combination with an oxide coating to reduce crack formation. However, such steel inserts have likewise no great reinforcing capability for countering mechanical stresses. It should also be noted that in the known arrangements there are separate inserts (see e.g. FR-A-2 059 230), often at least two of them, for each cylinder. This results in cylinder head casting problems pertaining to the alignment and fixing of the inserts in the required position. This problem is further accentuated in the case of multi-cylinder cylinder heads. Working with inserts and the fastening of inserts takes time and requires great precision, with attendant extra costs. In the worst case it may happen that some inserts may be omitted, particularly in multi-cylinder engines, which leads to a substantial reduction in strength. This problem is eliminated by the reinforcement according to the invention consisting of a single piece for all the cylinders in a multi-cylinder cylinder head. In a particularly preferred embodiment the elongated reinforcing plate is provided with transverse arms which stretch between the valve ports. This results in further strengthening of the most stressed points. To improve anchoring in the light metal material, the reinforcement incorporates broadened anchoring portions. BRIEF DESCRIPTION OF THE DRAWINGS A more detailed description of a specific embodiment is given below with reference to the attached drawings, in which: Fig.1 shows in perspective one end of a cylinder head for a multi-cylinder engine. Fig.2 shows an axial section through the cylinder head depicted in Fig.1. Fig.3 shows a cross-section on a somewhat larger scale through the cylinder head depicted in Fig.2. Fig.4 shows a view from above which for the sake of clarity depicts only the valve port orifices and the reinforcement according to the invention. Fig.5 shows in simplified form an alternative embodiment of the valve port orifices and the reinforcement in Fig.4. DETAILED DESCRIPTION OF AN EMBODIMENT Fig.1 depicts schematically the end portion of a cylinder head 1 in which four combustion chambers 2a, 2b, 2c, 2d are visible. Each combustion chamber 2a incorporates the orifices of four valve ports 3a, 4a, 5a, 6a, but for the sake of clarity only one cylinder is depicted with the references. The other combustion chambers in the cylinder head are of the same design and therefore require no further discussion. Two of the ports are inlet ports, while the other two are exhaust gas ports. As most clearly visible in Fig.4, the port orifices are arranged substantially symmetrically in a four-leaf clover pattern about the central axis. In the middle of each of the combustion chambers 2a, 2b, 2c, 2d there is an aperture 5 for an ignition device. The cylinder head 1 also incorporates in the traditional manner (but not depicted in detail) cooling ducts, connections for manifolds, controls for valves, camshaft bearings, etc. An elongated and relatively narrow reinforcing plate 6 stretches, as shown in Fig.2, along all the cylinders 2a, 2b, 2c, 2d and is embedded so as to follow the contours of the combustion chambers at a depth of a few centimetres. As depicted in Fig.2, the reinforcing plate 6 has an undulating contour. As best visible in Fig.4, the reinforcing plate 6 stretches in the form of a narrow wavy strip between the central axes of the combustion chambers. To improve the anchoring of the reinforcing plate 6 in the light alloy material, it incorporates enlarged or broadened portions 7 on both sides of each valve port group. For each cylinder there is a transverse arm 8 which is firmly connected, e.g. by riveting or spot welding, to the elongated reinforcement 6. The elongated reinforcement 6 and the transverse arms 8 may also be manufactured as a single piece. The transverse arms 8 start from the region of the combustion chamber central axis and stretch cruciformly out perpendicularly from both sides of the reinforcing plate 6 (Fig.4). The middle portion 9 of the transverse arms 8 is enlarged to improve the strengthening effect in the central region. The middle portion 9 is also provided with a hole (not shown in the figures) running through it for an ignition device. The transverse arms 8 also incorporate, exactly as the reinforcing plate 6 does, enlarged or broadened portions 10 to improve the anchoring in the host material. As may be seen in Fig.3, the transverse arms 8 also follow the cylinder head contour and form a spread V-shape in a section perpendicular to the central axis of the cylinder head 1 between the ports. There is thus a reinforcing element along each valve port aperture, while the region around the central axis of the cylinders contains a large reinforcement portion 9. The reinforcing structure according to the invention thus provides the weakest portions with effective strengthening, while the fitting and fastening of the reinforcement in the casting mould remains extremely easy because the structure is cast in a single piece. The material of the reinforcement is of course stronger than the light metal alloy casting which constitutes the cylinder head 1. It is advantageous for the reinforcement to be made of steel plate but other materials may of course be considered. To improve bonding between the cast-in reinforcement and the host material, the reinforcement may be protected with a fusible coating which has a lower melting point than the light metal alloy. The protective alloy will then melt away during the casting process and leave a surface free from oxide. ALTERNATIVE EMBODIMENTS OF THE INVENTION It will be obvious to specialists that the reinforcement according to the invention may be modified in various ways within the scope of the patent claims. For example, the reinforcement may incorporate additional broadened portions or be provided with protrusions, holes or flanges for better anchoring in the host material. Its shape may also differ from the narrow strip with rectangular cross-section depicted in the drawings. For example, an oval or circular cross-section is conceivable. There may also be additional transverse arms arranged between the valve port groups etc. The port orifices 3a, 4a, 5a and 6a are, as previously mentioned, arranged substantially symmetrically in a four-leaf clover pattern about the central axis. Fig.4 shows one possibility for the placing of the port orifices. It is of course possible to place the port orifices in a different manner, e.g. as shown in Fig.5, without departing from the four-leaf clover arrangement. In Fig.5 the reinforcing element is shown stretching, in the same manner as in Fig.4, between two valve pairs which cooperate with respective cylinder spaces 2a, 2b, 2c and 2d, and the transverse arms 8 are shown stretching out from the central axis region between the valve port apertures.

Claims: Multi-cylinder cylinder head (1) of light metal, such as aluminium and aluminium alloy, for a combustion engine, characterised in that a longitudinal reinforcing element (6) made of a mechanically stronger material than the aforesaid light metal is embedded in the light metal and stretches in one piece along all the cylinders. Cylinder head according to claim 1, characterised in that the reinforcing element (6) consists of an elongated relatively narrow steel plate. Cylinder head according to claim 1 or 2, characterised in that the reinforcing element (6) exhibits broadened or enlarged anchoring portions (7). Cylinder head according to claims 1-3, characterised in that the reinforcing element (6) is provided with transverse arms (8). Cylinder head according to claim 4, characterised in that the transverse arms stretch substantially perpendicularly to the longitudinal direction of the reinforcing element (6). Cylinder head according to claim 4 or 5, incorporating four valve ports (3a, 4a, 5a, 6a) arranged substantially symmetrically about the central axis of each combustion chamber (2a, 2b, 2c, 2d), characterised in that the reinforcing element (6) stretches between two pairs of valve ports which cooperate with respective combustion chambers (2a, 2b, 2c, 2d) and that the transverse arms (8) stretch out from the central axis region between the valve port apertures. Cylinder head according to one of claims 4 to 6, charcterised in that the transverse arms (8) incorporate broadened or enlarged anchoring portions (10).

Inventors: SAEAEF LARS, STENFORS SVEN-ERIC, SAEAEF, LARS, STENFORS, SVEN-ERIC, Sääf, Lars
Applicants: SAAB AUTOMOBILE, SAAB AUTOMOBILE AKTIEBOLAG
Application year: 1994
Main classification: F02F1
IPC codes: B22D19, F02F1